While the recent drive for higher integration densities and operating speeds in LSI devices makes it necessary to further reduce the pattern rule, deep-UV lithography has been investigated as the advanced micropatterning technology. Among others, the KrF or ArF excimer laser lithography is developed as an essential technology for micropatterning to a feature size of 0.3 μm or less and has been utilized in a commercial scale.
With respect to chemically amplified positive resist compositions adapted for the photolithography using excimer laser light, specifically KrF excimer laser light of 253 nm wavelength or ArF excimer laser light of 193 nm wavelength as a light source, the primary requirement is, of course, a high transparency at the relevant wavelength. They are also required to meet a high etch resistance sufficient to comply with film thickness reduction, a high sensitivity sufficient to minimize the burden to expensive optical materials, and among others, a high resolution sufficient to form an accurate fine pattern. The key to fulfill these requirements is to develop a base resin featuring high transparency, high rigidity and high reactivity. Active efforts have been devoted for such development, with some fruitful results being available. Active studies are also made on ArF immersion, EUV and EB lithography. In the current situation taking further steps toward miniaturization, not only a higher resolution is required, but it is one of important tasks to reduce irregularities on pattern sidewalls, known as line edge roughness (LER).
One means for improving the resolution and LER of chemically amplified positive resist compositions used in the excimer laser photolithography is by adding an acid-decomposable low molecular weight compound. Known are acid-decomposable ester compounds having a hydroxyl or ester group and a steroid structure which are decomposed under the action of acid to increase their solubility in alkaline developer. See JP-A H06-236033, JP 3944669, and JP 3988517, for example. However, resist compositions comprising these compounds are still insufficient in improving LER, or are sometimes degraded in resolution as the feature size is further reduced. A further improvement is desired.
Citation List
    Patent Document 1: JP-A H06-236033    Patent Document 2: JP 3944669 (U.S. Pat. No. 6,448,420)    Patent Document 3: JP 3988517 (U.S. Pat. No. 6,821,705)